Lifetime OLED display

ABSTRACT

Light emitting devices including sub-pixels having different numbers of emissive layers are provided. At least one sub-pixel of a first color may include a single emissive layer, and at least one sub-pixel of a second color may include multiple emissive layers disposed in a vertical stack. Light emitting devices in which different voltages are applied to each sub-pixel or group of sub-pixels are also provided. In some configurations, the voltage to be applied to a sub-pixel may be selected based upon the number of emissive layers in the sub-pixel.

The claimed invention was made by, on behalf of, and/or in connectionwith one or more of the following parties to a joint universitycorporation research agreement: Regents of the University of Michigan,Princeton University, The University of Southern California, and theUniversal Display Corporation. The agreement was in effect on and beforethe date the claimed invention was made, and the claimed invention wasmade as a result of activities undertaken within the scope of theagreement.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.13/615,666, filed Sep. 14, 2012, the disclosure of which is incorporatedby reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to organic light emitting devices and,more specifically, to organic light emitting devices that use stackedsub-pixels to improve or enhance device lifetime and/or performance.

BACKGROUND

Opto-electronic devices that make use of organic materials are becomingincreasingly desirable for a number of reasons. Many of the materialsused to make such devices are relatively inexpensive, so organicopto-electronic devices have the potential for cost advantages overinorganic devices. In addition, the inherent properties of organicmaterials, such as their flexibility, may make them well suited forparticular applications such as fabrication on a flexible substrate.Examples of organic opto-electronic devices include organic lightemitting devices (OLEDs), organic phototransistors, organic photovoltaiccells, and organic photodetectors. For OLEDs, the organic materials mayhave performance advantages over conventional materials. For example,the wavelength at which an organic emissive layer emits light maygenerally be readily tuned with appropriate dopants.

OLEDs make use of thin organic films that emit light when voltage isapplied across the device. OLEDs are becoming an increasinglyinteresting technology for use in applications such as flat paneldisplays, illumination, and backlighting. Several OLED materials andconfigurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and5,707,745, which are incorporated herein by reference in their entirety.

One application for phosphorescent emissive molecules is a full colordisplay. Industry standards for such a display call for pixels adaptedto emit particular colors, referred to as “saturated” colors. Inparticular, these standards call for saturated red, green, and bluepixels. Color may be measured using CIE coordinates, which are wellknown to the art.

One example of a green emissive molecule is tris(2-phenylpyridine)iridium, denoted Ir(ppy)₃, which has the following structure:

In this, and later figures herein, we depict the dative bond fromnitrogen to metal (here, Ir) as a straight line.

As used herein, the term “organic” includes polymeric materials as wellas small molecule organic materials that may be used to fabricateorganic opto-electronic devices. “Small molecule” refers to any organicmaterial that is not a polymer, and “small molecules” may actually bequite large. Small molecules may include repeat units in somecircumstances. For example, using a long chain alkyl group as asubstituent does not remove a molecule from the “small molecule” class.Small molecules may also be incorporated into polymers, for example as apendent group on a polymer backbone or as a part of the backbone. Smallmolecules may also serve as the core moiety of a dendrimer, whichconsists of a series of chemical shells built on the core moiety. Thecore moiety of a dendrimer may be a fluorescent or phosphorescent smallmolecule emitter. A dendrimer may be a “small molecule,” and it isbelieved that all dendrimers currently used in the field of OLEDs aresmall molecules.

As used herein, “top” means furthest away from the substrate, while“bottom” means closest to the substrate. Where a first layer isdescribed as “disposed over”, “deposited over” a second layer, the firstlayer is disposed further away from substrate. There may be other layersbetween the first and second layer, unless it is specified that thefirst layer is “in contact with” the second layer. For example, acathode may be described as “disposed over” an anode, even though thereare various organic layers in between.

As used herein, “solution processible” means capable of being dissolved,dispersed, or transported in and/or deposited from a liquid medium,either in solution or suspension form.

A ligand may be referred to as “photoactive” when it is believed thatthe ligand directly contributes to the photoactive properties of anemissive material. A ligand may be referred to as “ancillary” when it isbelieved that the ligand does not contribute to the photoactiveproperties of an emissive material, although an ancillary ligand mayalter the properties of a photoactive ligand.

As used herein, and as would be generally understood by one skilled inthe art, a first “Highest Occupied Molecular Orbital” (HOMO) or “LowestUnoccupied Molecular Orbital” (LUMO) energy level is “greater than” or“higher than” a second HOMO or LUMO energy level if the first energylevel is closer to the vacuum energy level. Since ionization potentials(IP) are measured as a negative energy relative to a vacuum level, ahigher HOMO energy level corresponds to an IP having a smaller absolutevalue (an IP that is less negative). Similarly, a higher LUMO energylevel corresponds to an electron affinity (EA) having a smaller absolutevalue (an EA that is less negative). On a conventional energy leveldiagram, with the vacuum level at the top, the LUMO energy level of amaterial is higher than the HOMO energy level of the same material. A“higher” HOMO or LUMO energy level appears closer to the top of such adiagram than a “lower” HOMO or LUMO energy level.

As used herein, and as would be generally understood by one skilled inthe art, a first work function is “greater than” or “higher than” asecond work function if the first work function has a higher absolutevalue. Because work functions are generally measured as negative numbersrelative to vacuum level, this means that a “higher” work function ismore negative. On a conventional energy level diagram, with the vacuumlevel at the top, a “higher” work function is illustrated as furtheraway from the vacuum level in the downward direction. Thus, thedefinitions of HOMO and LUMO energy levels follow a different conventionthan work functions.

More details on OLEDs, and the definitions described above, can be foundin U.S. Pat. No. 7,279,704, which is incorporated herein by reference inits entirety.

SUMMARY OF THE INVENTION

Embodiments of the invention provide devices having sub-pixels thatincorporate different numbers of emissive layers. In an embodiment, apixel within a light-emitting region of a device includes multiplesub-pixels. At least one of the sub-pixels includes a single emissivelayer of a first color, and at least one of the sub-pixels of a secondcolor includes multiple emissive layers disposed in a stack.

In embodiment, a device includes a first sub-pixel having an emissivelayer with a first peak emission wavelength and a second sub-pixelhaving multiple emissive layers, each with a peak emission wavelengthdifferent from the first peak emission wavelength, where the secondsub-pixel has a different number of emissive layers than the firstsub-pixel. The emissive layers in the second sub-pixel may include thesame emissive material, and/or may have the same or substantially thesame peak emission wavelength.

In an embodiment, a device includes first and second sub-pixels, each ofwhich is provided with a different voltage. The voltages may be providedby separate and independent power supplies, or may be provided by acommon power supply and connecting circuit. Each sub-pixel may have adifferent number of emissive layers than the other.

In an embodiment, a pixel of a light-emitting device includes first,second, and third sub-pixels of different colors and having m, n, and pemissive layers, respectively, where m is not equal to n and n is notequal to p.

Device types according to embodiments may include full-color displays,mobile devices, consumer products having flexible displays, consumerproduct having transparent displays, portable devices, tablet devices,smart phones, illumination devices, wireless handheld devices, andtelevisions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic light emitting device.

FIG. 2 shows an inverted organic light emitting device that does nothave a separate electron transport layer.

FIG. 3 shows example sub-pixels according to an embodiment of theinvention including a sub-pixel with multiple emissive layers.

FIG. 4 shows example sub-pixels according to an embodiment of theinvention including a sub-pixel with multiple emissive layers.

FIG. 5A shows an example simplified schematic according to an embodimentof the invention, in which a single voltage source is used to provide apower supply to two sub-pixels.

FIG. 5B shows an example simplified schematic according to an embodimentof the invention in which separate power supplies provide power toassociated separate sub-pixels.

FIG. 6A shows an example of a portion of a color tunable and/or colortemperature tunable lighting panel having sub-pixel stripes of yellowand blue according to an embodiment of the invention.

FIG. 6B shows an example of a portion of a color tunable and/or colortemperature tunable lighting panel having sub-pixel stripes of red,green, and blue according to an embodiment of the invention.

DETAILED DESCRIPTION

Generally, an OLED comprises at least one organic layer disposed betweenand electrically connected to an anode and a cathode. When a current isapplied, the anode injects holes and the cathode injects electrons intothe organic layer(s). The injected holes and electrons each migratetoward the oppositely charged electrode. When an electron and holelocalize on the same molecule, an “exciton,” which is a localizedelectron-hole pair having an excited energy state, is formed. Light isemitted when the exciton relaxes via a photoemissive mechanism. In somecases, the exciton may be localized on an excimer or an exciplex.Non-radiative mechanisms, such as thermal relaxation, may also occur,but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from theirsinglet states (“fluorescence”) as disclosed, for example, in U.S. Pat.No. 4,769,292, which is incorporated by reference in its entirety.Fluorescent emission generally occurs in a time frame of less than 10nanoseconds.

More recently, OLEDs having emissive materials that emit light fromtriplet states (“phosphorescence”) have been demonstrated. Baldo et al.,“Highly Efficient Phosphorescent Emission from OrganicElectroluminescent Devices,” Nature, vol. 395, 151-154, 1998;(“Baldo-I”) and Baldo et al., “Very high-efficiency green organiclight-emitting devices based on electrophosphorescence,” Appl. Phys.Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), which are incorporatedby reference in their entireties. Phosphorescence is described in moredetail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporatedby reference.

FIG. 1 shows an organic light emitting device 100. The figures are notnecessarily drawn to scale. Device 100 may include a substrate 110, ananode 115, a hole injection layer 120, a hole transport layer 125, anelectron blocking layer 130, an emissive layer 135, a hole blockinglayer 140, an electron transport layer 145, an electron injection layer150, a protective layer 155, a cathode 160, and a barrier layer 170.Cathode 160 is a compound cathode having a first conductive layer 162and a second conductive layer 164. Device 100 may be fabricated bydepositing the layers described, in order. The properties and functionsof these various layers, as well as example materials, are described inmore detail in U.S. Pat. No. 7,279,704 at cols. 6-10, which areincorporated by reference.

More examples for each of these layers are available. For example, aflexible and transparent substrate-anode combination is disclosed inU.S. Pat. No. 5,844,363, which is incorporated by reference in itsentirety. An example of a p-doped hole transport layer is m-MTDATA dopedwith F.sub.4-TCNQ at a molar ratio of 50:1, as disclosed in U.S. PatentApplication Publication No. 2003/0230980, which is incorporated byreference in its entirety. Examples of emissive and host materials aredisclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which isincorporated by reference in its entirety. An example of an n-dopedelectron transport layer is BPhen doped with Li at a molar ratio of 1:1,as disclosed in U.S. Patent Application Publication No. 2003/0230980,which is incorporated by reference in its entirety. U.S. Pat. Nos.5,703,436 and 5,707,745, which are incorporated by reference in theirentireties, disclose examples of cathodes including compound cathodeshaving a thin layer of metal such as Mg:Ag with an overlyingtransparent, electrically-conductive, sputter-deposited ITO layer. Thetheory and use of blocking layers is described in more detail in U.S.Pat. No. 6,097,147 and U.S. Patent Application Publication No.2003/0230980, which are incorporated by reference in their entireties.Examples of injection layers are provided in U.S. Patent ApplicationPublication No. 2004/0174116, which is incorporated by reference in itsentirety. A description of protective layers may be found in U.S. PatentApplication Publication No. 2004/0174116, which is incorporated byreference in its entirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210,a cathode 215, an emissive layer 220, a hole transport layer 225, and ananode 230. Device 200 may be fabricated by depositing the layersdescribed, in order. Because the most common OLED configuration has acathode disposed over the anode, and device 200 has cathode 215 disposedunder anode 230, device 200 may be referred to as an “inverted” OLED.Materials similar to those described with respect to device 100 may beused in the corresponding layers of device 200. FIG. 2 provides oneexample of how some layers may be omitted from the structure of device100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided byway of non-limiting example, and it is understood that embodiments ofthe invention may be used in connection with a wide variety of otherstructures. The specific materials and structures described areexemplary in nature, and other materials and structures may be used.Functional OLEDs may be achieved by combining the various layersdescribed in different ways, or layers may be omitted entirely, based ondesign, performance, and cost factors. Other layers not specificallydescribed may also be included. Materials other than those specificallydescribed may be used. Although many of the examples provided hereindescribe various layers as comprising a single material, it isunderstood that combinations of materials, such as a mixture of host anddopant, or more generally a mixture, may be used. Also, the layers mayhave various sublayers. The names given to the various layers herein arenot intended to be strictly limiting. For example, in device 200, holetransport layer 225 transports holes and injects holes into emissivelayer 220, and may be described as a hole transport layer or a holeinjection layer. In one embodiment, an OLED may be described as havingan “organic layer” disposed between a cathode and an anode. This organiclayer may comprise a single layer, or may further comprise multiplelayers of different organic materials as described, for example, withrespect to FIGS. 1 and 2.

Structures and materials not specifically described may also be used,such as OLEDs comprised of polymeric materials (PLEDs) such as disclosedin U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated byreference in its entirety. By way of further example, OLEDs having asingle organic layer may be used. OLEDs may be stacked, for example asdescribed in U.S. Pat. No. 5,707,745 to Forrest et al, which isincorporated by reference in its entirety. The OLED structure maydeviate from the simple layered structure illustrated in FIGS. 1 and 2.For example, the substrate may include an angled reflective surface toimprove out-coupling, such as a mesa structure as described in U.S. Pat.No. 6,091,195 to Forrest et al., and/or a pit structure as described inU.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated byreference in their entireties.

Unless otherwise specified, any of the layers of the various embodimentsmay be deposited by any suitable method. For the organic layers,preferred methods include thermal evaporation, ink-jet, such asdescribed in U.S. Pat. Nos. 6,013,982 and 6,087,196, which areincorporated by reference in their entireties, organic vapor phasedeposition (OVPD), such as described in U.S. Pat. No. 6,337,102 toForrest et al., which is incorporated by reference in its entirety, anddeposition by organic vapor jet printing (OVJP), such as described inU.S. patent application Ser. No. 10/233,470, which is incorporated byreference in its entirety. Other suitable deposition methods includespin coating and other solution based processes. Solution basedprocesses are preferably carried out in nitrogen or an inert atmosphere.For the other layers, preferred methods include thermal evaporation.Preferred patterning methods include deposition through a mask, coldwelding such as described in U.S. Pat. Nos. 6,294,398 and 6,468,819,which are incorporated by reference in their entireties, and patterningassociated with some of the deposition methods such as ink jet and OVJD.Other methods may also be used. The materials to be deposited may bemodified to make them compatible with a particular deposition method.For example, substituents such as alkyl and aryl groups, branched orunbranched, and preferably containing at least 3 carbons, may be used insmall molecules to enhance their ability to undergo solution processing.Substituents having 20 carbons or more may be used, and 3-20 carbons isa preferred range. Materials with asymmetric structures may have bettersolution processibility than those having symmetric structures, becauseasymmetric materials may have a lower tendency to recrystallize.Dendrimer substituents may be used to enhance the ability of smallmolecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the presentinvention may further optionally comprise a barrier layer. One purposeof the barrier layer is to protect the electrodes and organic layersfrom damaging exposure to harmful species in the environment includingmoisture, vapor and/or gases, etc. The barrier layer may be depositedover, under or next to a substrate, an electrode, or over any otherparts of a device including an edge. The barrier layer may comprise asingle layer, or multiple layers. The barrier layer may be formed byvarious known chemical vapor deposition techniques and may includecompositions having a single phase as well as compositions havingmultiple phases. Any suitable material or combination of materials maybe used for the barrier layer. The barrier layer may incorporate aninorganic or an organic compound or both. The preferred barrier layercomprises a mixture of a polymeric material and a non-polymeric materialas described in U.S. Pat. No. 7,968,146, PCT Pat. Application Nos.PCT/US2007/023098 and PCT/US2009/042829, which are herein incorporatedby reference in their entireties. To be considered a “mixture”, theaforesaid polymeric and non-polymeric materials comprising the barrierlayer should be deposited under the same reaction conditions and/or atthe same time. The weight ratio of polymeric to non-polymeric materialmay be in the range of 95:5 to 5:95. The polymeric material and thenon-polymeric material may be created from the same precursor material.In one example, the mixture of a polymeric material and a non-polymericmaterial consists essentially of polymeric silicon and inorganicsilicon.

Devices fabricated in accordance with embodiments of the invention maybe incorporated into a wide variety of consumer products, including flatpanel displays, computer monitors, medical monitors, televisions,billboards, lights for interior or exterior illumination and/orsignaling, heads up displays, fully transparent displays, flexibledisplays, laser printers, telephones, cell phones, personal digitalassistants (PDAs), laptop computers, digital cameras, camcorders,viewfinders, micro-displays, vehicles, a large area wall, theater orstadium screen, or a sign. Various control mechanisms may be used tocontrol devices fabricated in accordance with the present invention,including passive matrix and active matrix. Many of the devices areintended for use in a temperature range comfortable to humans, such as18 degrees C. to 30 degrees C., and more preferably at room temperature(20-25 degrees C.).

The materials and structures described herein may have applications indevices other than OLEDs. For example, other optoelectronic devices suchas organic solar cells and organic photodetectors may employ thematerials and structures. More generally, organic devices, such asorganic transistors, may employ the materials and structures.

The terms halo, halogen, alkyl, cycloalkyl, alkenyl, alkynyl, arylkyl,heterocyclic group, aryl, aromatic group, and heteroaryl are known tothe art, and are defined in U.S. Pat. No. 7,279,704 at cols. 31-32,which are incorporated herein by reference.

Some OLED displays and similar devices may have lifetimes limited by thelifetime of one or more sub-pixel types. For example, some conventionaldisplays use a display region having multiple pixels, where each pixelincludes at least one red, green, and blue sub-pixel. One colorsub-pixel, most commonly blue, will typically have a shorter averagelifetime than the the other sub-pixels, thus limiting the lifetime ofthe device as a whole.

It has been found that the lifetime of a sub-pixel device may beincreased by using a stacked device configuration. In such a device, theluminance provided by each emissive layer of the device, as well as thecurrent through the layer, may be reduced, thus increasing the lifetimeof the device. In an embodiment of the invention, fewer than all of thesub-pixels in a region may use a stacked configuration. For example, adevice may use single emissive layer red and green sub-pixels, andstacked blue sub-pixels. As used herein, a “single emissive layer”device refers to a device that includes only a single emissive regiondisposed between two electrodes, without second or additional emissiveregions disposed between the electrodes. Configurations having at leastone stacked sub-pixel, but fewer than all of the sub-pixels in a stackedconfiguration, may allow for improved device lifetime with minimal orlimited increase in cost and manufacturing complexity. In some casesthis may allow for an increase in the lifetime of the device by up to afactor of three, as well as reducing the power consumption of a displayby up to approximately 15%. The architectures disclosed herein also mayprovide improved display lifetime but without a significant increase inproduct cost. For example, various arrangements disclosed herein may beimplemented with not more than about a 50% increase in Total AverageCycle Time (TACT) over conventional displays, or not more than about a50% increase in capital cost of an OLED deposition system.Implementations of the techniques disclosed herein also may require nochange or minimal change of the OLED backplane relative to aconventional backplane. For example, some implementations may combinepixel anode column connections to two external connections instead ofone, while leaving other architecture details unchanged relative toconventional fabrication techniques and arrangements. As anotherexample, multiple power supplies or power supply voltages may be usedinstead of the single source, single-voltage power supply common toconventional display devices, to allow different voltages to be providedto sub-pixels having different stack sizes.

More generally, embodiments of the invention may use sub-pixels havingvarious numbers of emissive layers. That is, sub-pixels of a first colormay have m emissive layers, and sub-pixels of a second, different color,may have n emissive layers, where n>m. Sub-pixels of a third color mayhave m or n emissive layers, or may have a number of emissive layers pdifferent from both m and n. As used herein, a sub-pixel is consideredto be a specific color when it has a peak emission wavelength of thatcolor, or within a range associated with the color. As used herein, eachsub-pixel in a pixel may be independently addressable, i.e., it may beindividually controlled by selectively applying current to thesub-pixel.

In general, embodiments of the invention may provide an organic lightemitting device having multiple sub-pixels. Each sub-pixel may includean anode, a cathode, and one or more organic emissive layers disposedbetween the anode and the cathode. Devices having multiple organicemissive layers may include internal electrodes or similar layers, suchas where an electrode is disposed between an anode and a cathode, and anorganic emissive layer is disposed between each pair of the anode andthe internal electrode, and the internal electrode and the cathode. Theorganic emissive layer may include a host and a dopant such as aphosphorescent dopant as disclosed herein.

FIG. 3 shows example sub-pixel devices according to an embodiment of theinvention. For clarity, only three sub-pixels 301, 302, 303 are shown,though it will be understood that a device as disclosed herein mayinclude any number of sub-pixels that may be addressed in various waysto form multiple pixels, such as within a full-color display or similardevice. The devices are disposed on a substrate 300, over which each ofthe layers shown may be deposited in order, as previously describedherein. Each sub-pixel includes a first electrode 314, 324, 334 disposedover the substrate and a second electrode 312, 322, 332 disposed overthe first electrode. Emissive regions 310, 320, and 330 may be disposedover the respective first electrode. Sub-pixels such as those shown inFIGS. 3 and 4 may be described herein as containing one or more emissivelayers and the emissive regions 310, 320, 330, and so on may be referredto as emissive layers, though it will be understood that more generallythese regions may include other layers as described. More specifically,the emissive regions may include an emissive layer as well as otherlayers disclosed herein, such as transport layers, blocking layers, andthe like. Each emissive layer may be characterized by an emissionspectrum with a peak wavelength, which may be selected to provide adesired color of visible light when a current is applied. The selectionof specific materials, including dopants such as phosphorescent dopants,to obtain a desired emission color will be well understood by one ofskill in the art.

Sub-pixel 303 shows an example of multiple emissive layers 330, 340 in asub-pixel. An internal electrode 336 or other interface may be disposedbetween the emissive layers 330, 340. As previously described, otherlayers may be disposed between each pair of electrodes 332 and 336, and336 and 334. The sub-pixel 303 may be referred to as a “stacked” device,the operation of which will be readily understood by one of skill in theart. Each sub-pixel 301, 302, 303 may emit a different color of light.For example, the sub-pixels may emit red, green, and blue lightrespectively. The stacked device 303 may be configured to emit anydesired color of light. Typically the stacked device 303 is configuredto emit light that otherwise would be the limiting factor in thelifetime of a device in which the sub-pixels 301, 302, 303 areincorporated. For example, where a single emissive layer blue devicewould otherwise have the shortest lifetime compared to the sub-pixels301, 302, it is preferably to configure the stacked device 303 to emitblue light.

More generally, each sub-pixel in a multi-pixel arrangement in whichsub-pixels emit different colors of light may be configured with anydesired number of emissive layers, to obtain desired lifetimes of thesub-pixels and, therefore, the device as a whole. For example, in someconfigurations it may be found that blue devices have the lowest averagelifetime, red devices the next lowest, and green devices the highestlifetime. Accordingly, blue and red sub-pixels may be configured to usemultiple emissive layers, and green sub-pixels to use single emissivelayers. In some cases, the number of emissive layers may be selectedbased upon the relative resulting lifetimes and/or power requirements.Continuing the previous example, blue sub-pixels may be configured withthree or more emissive layers, red sub-pixels with two or more emissivelayers, and green sub-pixels with one or more emissive layers.

In an embodiment, a light-emitting region of a device may include one ormore pixels. Each pixel may include a first sub-pixel, such as sub-pixel301, having a first emissive layer having a first peak emissionwavelength, such as emissive layers 310, 320. The pixel also may includea second sub-pixel, such as sub-pixel 302, having a second emissivelayer with a second peak emission wavelength different from the firstpeak emission wavelength, such as emissive layer 330, and a thirdemissive layer with a third peak emission wavelength different from thefirst peak emission wavelength, such as emissive layer 340. The thirdemissive layer may be disposed over the second emissive layer to form astacked device as previously described. It may be preferred for thefirst emissive layer to be a red or green emissive layer, and for thesecond and third emissive layers to be blue emissive layers. The pixelmay include additional sub-pixels. For example, the pixel may include athird sub-pixel such as sub-pixel 302. The third sub-pixel may have afourth emissive layer, such as emissive layer 320, with a fourth peakemission wavelength different from each of the first, second, and thirdpeak emission wavelengths. Where the first emissive layer is a red orgreen emissive layer, it may be preferred for the fourth emissive layerto be green or red, respectively.

The second sub-pixel may include additional emissive layers, such aswhere a fourth emissive layer with a fourth peak emission wavelengthdifferent from the first peak emission wavelength is disposed over thethird emissive layer. The additional layers may be the same color orsubstantially the same color as the second emissive layer. For example,the fourth peak emission wavelength may be equal to, substantially equalto, or within a threshold range of the first peak emission wavelength.As a specific example, the fourth peak emission wavelength may be within10%, more preferably 5%, of the second peak emission wavelength. Thus,the color emitted by each emissive layer in a stacked sub-pixel may bevisibly the same or substantially the same color.

FIG. 4 shows example sub-pixel devices according to an embodiment of theinvention, in which one sub-pixel includes three emissive layers 330,340, 420. The structure of each sub-pixel 301, 302, 403 is similar tothe structure shown and described with respect to FIG. 3. In contrast toFIG. 3, sub-pixel 403 includes an additional internal electrode orsimilar layer 406 and an additional emissive layer 420. Thus, similar tothe stacked device 303 of FIG. 3, the stacked device 403 includesmultiple emissive layers, which may provide improved lifetime relativeto a single emissive layer device.

Displays and other devices may include multiple groups of sub-pixels asshown in FIGS. 3-4, which may be logically addressed as individualpixels as disclosed herein and as will be readily understood by one ofskill in the art. The specific arrangements and groupings of sub-pixelsshown in FIGS. 3-4 are illustrative only, and various other arrangementsmay be used. In some configurations, physical sub-pixels may be sharedbetween two or more logical pixels, such as where a larger red, green,or blue sub-pixel is grouped with two sets of sub-pixels of the othertwo colors, to form two separately-addressable logical pixels. Otherarrangements may be used, such as those disclosed in U.S. PatentApplication Pub. No. 2011/0127506, the disclosure of which isincorporated by reference in its entirety, and as will be readilyunderstood by one of skill in the art.

The individual emissive regions within a stacked device also may bereferred to as devices or sub-devices. For example, referring to FIG. 3,each emissive layer 330, 340 may be considered to be an emissive layerwithin a sub-device 350, 360, respectively. Each sub-device may bedefined by a first and second electrode or similar layer, such as layers332, 336 which define sub-device 350. Similarly, layers 334, 336 may beconsidered as the boundaries of the sub-device 360.

To fabricate a partially-stacked device as disclosed herein, any initialcommon layers may be deposited, followed by various combinations ofemissive layers and/or additional common layers. For example, afterdepositing one or more layers common to each sub-pixel, such as thelayers below the emissive layer in FIGS. 1-2, a first emissive layer maybe deposited for a first type of sub-pixel, such as a red or greensub-pixel. A second type of emissive layer may be deposited after thefirst type. The first and second types of sub-pixels may be depositedusing, for example, masking processes or other patterning process suchas LITI, OVJP, or the like. A third type of emissive layer, such as forblue sub-pixels, may then be deposited locally over the appropriatesub-pixel regions, for example over anode pads designated for the bluesub-pixels. A stacked device may be built by depositing additionallayers, including additional emissive layers, over the desiredsub-pixels. For example, where a masking technique is used, the mask maybe left in in place so as to deposit an emissive layer and any adjacentlayers such as an ETL, followed by an internal electrode or similarlayer, upper HIL and/or HTL, and a second EML. The mask may then beremoved, and any additional common layers, such as blocking, ETL, and/orcathode layers, may be deposited. Similarly, where other patterningtechniques are used, additional layers of electrodes, emissive layers,transport layers, and the like may be deposited over an initial emissivelayer to form a stacked region having multiple emissive layers. Theapproach may be repeated to produce devices having two, three, or moreemissive layers.

In some implementations, two common power supplies may be used. Forexample, if a blue sub-pixel uses a stacked device and associated redand green sub-pixels use single emissive layer devices, then two commonpower supplies may be used. In such a configuration, a common cathodeconnection can be used for all three sub-pixels, and a separate anodesupply provided for the blue sub-pixel relative to the red and greenpixels. Thus, two common anode power supplies may be used per display.In general the anode power may be supplied to each sub-pixel throughpower lines running through each column of the display, and/or throughsub-pixels of the same color. Similar configurations may be used fordisplays that do not use standard column arrangements for the sub-pixelsas will readily be understood by one of skill in the art. The particularvoltages to be applied to different sub-pixels, and the arrangement ofpower supplies, may be selected based upon whether each sub-pixel isstacked and/or the number of emissive regions or sub-devices in thesub-pixel.

FIG. 5A shows an example simplified schematic according to an embodimentof the invention, in which a single voltage source is used to provide apower supply to two sub-pixels 510, 520. One sub-pixel 510 is a singleemissive layer device; the other sub-pixel 520 is a stacked device aspreviously described, which includes two emissive layers. The voltagesource 500 may provide power to both sub-pixels, by using connectingcircuitry 530 that adjusts the voltage applied to each of the sub-pixels510, 520.

Alternatively, separate voltage sources may be used for each sub-pixelor each type of sub-pixel, for example depending upon whether eachsub-pixel is a single emissive layer device or a stacked device. FIG. 5Bshows an example simplified schematic according to an embodiment of theinvention in which two separate power supplies 502, 503, provide powerto sub-pixels 510, 520, respectively.

More generally, a device according to an embodiment of the invention mayinclude first and second power sources that provide first and secondvoltages to first and second sub-pixels within the device, respectively.The power sources may be provided as separate and distinct powersupplies, such as power supplies 502, 503 in FIG. 5B. Alternatively, thepower sources may be provided by a single power supply 500 as shown inFIG. 5A, in conjunction with appropriate connecting circuitry 530. Theuse of multiple power supplies may allow for improved power consumptionover arrangements using a single power supply applied to both singleemissive layer sub-pixels and stacked sub-pixels. Generally, it may bedesirable to provide a higher voltage to a stacked device to obtain thesame luminance from the emissive portion of the sub-pixel as would beexpected in a single emissive layer device. However, if the highervoltage was also applied to the single emissive layer sub-pixel, itlikely would increase the power consumption of the system. The use of aseparate power supply for the single emissive layer sub-pixel orsub-pixels thus allows for optimization of the power consumption of theoverall system. If a single power supply was used to power allsub-pixels regardless of configuration, excess power likely would belost as heat within the system, which could negatively and undesirablyaffect the lifetime and/or power consumption of the system. The specificcircuitry that may be used in a particular configuration of sub-pixelswill be readily apparent to one of skill in the art.

It will be understood that the diagrams shown in FIGS. 5A and 5B aregreatly simplified for ease of illustration, and that in general anysuitable voltage source arrangement and associated circuitry may beused.

Sub-pixels may be disposed in various configurations as previouslydescribed. For example, the third sub-pixel may be disposed adjacent toone or both of the first and second sub-pixels. Multiple sub-pixels maybe arranged in columns, staggered rows, or other configurations.

In some configurations, the “pixels” and “sub-pixels” disclosed hereinmay refer to relatively large structures, such as “stripes” within alighting panel. In such a configuration, the pixels and sub-pixels maybe relatively large, since they may be used for illumination instead of,for example, a full-color display, or they may be around the same sizeas for displays and other devices as disclosed elsewhere herein. In anembodiment, a series of sets of red, green, and blue sub-pixels may beused to provide a color tunable and/or temperature tunable lightingpanel or similar device. For example, the device may include stripes ofred, green, and blue sub-pixels as described herein. Similarly, stripesof yellow and blue sub-pixels may be used within a lighting panel toachieve a similar effect. Each sub-pixel stripe or set of stripes mayhave arrangements as disclosed herein. For example, in a configurationhaving red, green, and blue sub-pixel stripes, the blue sub-pixel stripemay have a stacked configuration as disclosed herein, and the red andgreen stripes may use single emissive region arrangements. Moregenerally, any arrangement of stacked and single-layer devices asdisclosed herein may be used in the stripe configurations.

Each stripe may be a single sub-pixel as described, or it may includemultiple sub-pixels of the same color. Further, each stripe of the samecolor may be driven and/or controlled as a unit. Thus, the color and/orcolor temperature of the lighting panel may be adjusted by adjusting theoutput of each color within the panel. FIGS. 6A and 6B show examples ofportions of color tunable and/or color temperature tunable lightingpanels, having sub-pixel stripes of yellow and blue, or red, green, andblue, respectively. In each configuration, pixel stripes of the samecolor may be driven together. In conjunction, then, the different setsof same-color stripes may be driven to produce a desired color and/orcolor temperature.

In an embodiment, the sub-pixels may have shared or common layers, suchas where two or more emissive layers in different sub-pixels aredisposed over a single electrode layer, blocking layer, or other layer.A shared layer may be common between the single emissive layersub-pixels but not common with stacked sub-pixels, or it may be commonamong a stacked sub-pixel and one or more single emissive layersub-pixels.

As used herein, a “red” device or emissive layer has a peak emissionwavelength in the range of about 580-700 nm; a “green” device or layerhas a peak emission wavelength in the range of about 500-580 nm; and a“blue” device or layer has a peak emission wavelength in the range ofabout 400-500 nm.

Emissive regions, layers, and devices as disclosed herein may beincorporated into any suitable device or component, such as full-colordisplays, mobile devices, flat-panel displays, flexible displays,consumer products having a flexible and/or transparent display, tabletdevices, smart phones, illumination devices, wireless handheld devices,televisions, color-tunable lighting devices such as OLED lightingpanels, and the like.

It is understood that the various embodiments described herein are byway of example only, and are not intended to limit the scope of theinvention. For example, many of the materials and structures describedherein may be substituted with other materials and structures withoutdeviating from the spirit of the invention. The present invention asclaimed may therefore include variations from the particular examplesand preferred embodiments described herein, as will be apparent to oneof skill in the art. It is understood that various theories as to whythe invention works are not intended to be limiting.

The invention claimed is:
 1. A light-emitting device comprising: alight-emitting region comprising a pixel, the pixel comprising aplurality of sub-pixels; a first power source providing a first voltageto a first sub-pixel of the plurality of sub-pixels, wherein the firstsub-pixel includes a single emissive sub-device; and a second powersource providing a second voltage, different from the first voltage, toa second sub-pixel of the plurality of sub-pixels, wherein the secondsub-pixel comprises a stacked device, wherein the first power source isseparate and distinct from the second power source.
 2. The device ofclaim 1, wherein each sub-pixel of the plurality of sub-pixels thatcomprises a stacked device is provided power by the second power source.3. The device of claim 1, wherein each sub-pixel of the plurality ofsub-pixels that comprises a single emissive sub-device is provided powerby the first power source.
 4. The device of claim 1, wherein the firstpower source and the second power source are provided by a common powersupply and a connecting circuit.
 5. The device of claim 1, wherein thestacked device comprises a vertical stack.
 6. The device of claim 1,wherein the stacked device comprises a plurality of stacked emissivelayers.
 7. The device of claim 1, wherein the stacked device comprises aplurality of stacked emissive layers, and at least one layer of theplurality of stacked emissive layers comprises an organic emissivematerial.
 8. The device of claim 1, wherein the stacked device comprisesa plurality of vertically stacked emissive layers.
 9. The device ofclaim 1, wherein the stacked device comprises a plurality of verticallystacked sub-devices.
 10. The device of claim 1, wherein the stackeddevice comprises a plurality of vertically stacked emissive sub-devices.11. The device of claim 1, wherein the stacked device comprises aplurality of vertically stacked emissive sub-devices, and at least onesub-device of the plurality of vertically stacked emissive sub-devicescomprises an organic emissive material.
 12. The device of claim 1,wherein the first sub-pixel comprises a first emissive material having afirst peak emission wavelength, and the second sub-pixel comprises asecond emissive material having a having a second peak emissionwavelength, and wherein the second peak emission wavelength is differentthan the first peak emission wavelength.
 13. The device of claim 1,wherein the first sub-pixel comprises a first emissive material having afirst peak emission wavelength, and the second sub-pixel comprises asecond emissive material having a having a second peak emissionwavelength, wherein the second peak emission wavelength is differentthan the first peak emission wavelength, and wherein the first peakemission wavelength is in the range 580-700 nm.
 14. The device of claim1, wherein the first sub-pixel comprises a first emissive materialhaving a first peak emission wavelength, and the second sub-pixelcomprises a second emissive material having a having a second peakemission wavelength, wherein the second peak emission wavelength isdifferent than the first peak emission wavelength, and wherein the firstpeak emission wavelength is in the range 500-580 nm.
 15. The device ofclaim 1, wherein the first sub-pixel comprises a first emissive materialhaving a first peak emission wavelength, and the second sub-pixelcomprises a second emissive material having a having a second peakemission wavelength, wherein the second peak emission wavelength isdifferent than the first peak emission wavelength, and wherein thesecond peak emission wavelength is in the range 400-500 nm.
 16. Thedevice of claim 1, wherein the first sub-pixel comprises a firstemissive material having a first peak emission wavelength, and thesecond sub-pixel comprises a second emissive material having a having asecond peak emission wavelength, wherein the second peak emissionwavelength is different than the first peak emission wavelength, andwherein at least one emissive material selected from the groupconsisting of the first emissive material and the second emissivematerial, comprises an organic emissive material.
 17. The device ofclaim 1, wherein the device comprises a device of a type selected fromthe group consisting of: a consumer product having a color tunablelighting panel, a consumer product having color temperature tunablelighting panel, an illumination device, a color-tunable lighting device,and a color temperature tunable lighting device.
 18. The device of claim1, wherein the device comprises a device of a type selected from thegroup consisting of: a full-color display, a mobile device, a consumerproduct having a flexible display, a consumer product having atransparent display, a tablet device, a smart phone, a wireless handhelddevice, and a television.
 19. The device of claim 1, wherein the secondvoltage is greater than the first voltage.
 20. The device of claim 1,wherein the second voltage is greater than the first voltage, and aluminance of the first sub-pixel is substantially the same as aluminance of the second sub-pixel.
 21. A light-emitting devicecomprising: a light-emitting region comprising a pixel, the pixelcomprising a plurality of sub-pixels; a first power source providing afirst voltage to a first sub-pixel of the plurality of sub-pixels,wherein the first sub-pixel includes a single emissive sub-device; and asecond power source providing a second voltage, different from the firstvoltage, to a second sub-pixel of the plurality of sub-pixels, whereinthe second sub-pixel comprises a stacked device, wherein the firstsub-pixel comprises a first emissive material having a first peakemission wavelength, and the second sub-pixel comprises a secondemissive material having a having a second peak emission wavelength,wherein the second peak emission wavelength is different than the firstpeak emission wavelength, and wherein the first peak emission wavelengthis in a range selected from the group consisting of: 580-700 nm, 500-580nm, and 400-500 nm.